FWIW, I'm postponing any WordPress/CMS installation until I can come up with a path forward to migrate the forums data. Mostly it's because nothing modern will work on the old tools and libraries we are currently running. That said, I'm actively experimenting a lot behind the scenes to get some kind of migration going.
On the migration subject, I've found we have some nasty corupt values in our database tables from the early versions of vBulletin that didn't weather the upgrades very well. UTF-8 and non-UTF-8 data mixing together leads to all kinds of failures when importing to other systems. I doubt it'll break many hearts, but any not-UTF-8-safe characters will be stripped away in the process of whatever we migrate to. This typically manifests today as the "special" non-ASCII characters looking all garbled in some very old posts. For example, where you might expect "™" instead you'd see "â¢". Those garbled bits will just disappear.
Speaking of cleaning data, how would we feel about deleting a bunch of inactive users? I did a quick search and found that we have almost 7000 users with 0 or 1 post who have not been seen logged in for the last 365 days. Our total user list is just over 11000. Maybe also delete all the banned accounts that are labeled as "spammer".